1. Field of the Invention
The present invention relates to a hollow golf club head, and particularly relates to a golf club head having a wood type shape or another shape close to the wood type shape.
2. Description of the Related Art
Hollow golf club heads made from metal are used broadly as wood type golf club heads such as drivers or fairway woods. Generally, as shown in FIG. 3, a wood type hollow golf club head 1 includes a face portion 2 for hitting a ball therewith, a crown portion 3 forming the top portion of the golf club head, a sole portion 4 forming the bottom portion of the golf club head, a side portion 5 forming the side portion on the toe side, back side and heel side of the golf club head, and a hosel portion 6. A shaft 7 is inserted into the hosel portion 6 of the golf club head 1, and fixed thereto by an adhesive agent or the like. Incidentally, recently, many golf club heads called utility golf club heads have appeared on the market. As one kind of utility golf club head, various golf club heads similar to the wood type golf club head (that is, including a face portion, a sole portion, a side portion and a crown portion) are available on the market.
Aluminum alloys, stainless steel or titanium alloys are available as metal for forming such hollow golf club heads. Of them, titanium alloys have been used broadly in recent years.
JP-A-2002-119625 discloses a golf club head in which a face portion is made thicker than a crown portion, the crown portion is curved upward, and the face portion and the crown portion are molded integrally by press working.
JP-A-Hei.7-155410 discloses a golf club head in which the rear half side thereof is made from high-specific-gravity metal such as stainless steel or brass, while the front half side thereof is made from a low-specific-gravity material such as CFRP, titanium, or aluminum.
JP-A-Hei.7-112041 discloses a golf club head in which a crown portion is made from CFRP, and a sole portion is made from aluminum, while the other head body portion is made from stainless steel, a titanium alloy or a copper alloy.
In order to increase the carry of a shot with a metal hollow golf club head, development has been made and aimed at increasing the repulsion of a ball by use of bending of the face surface, to thereby hit the ball farther. However, when a golfer having a low head speed uses such a golf club head, the deformation of the face surface is so small that the effect of increasing the initial velocity of A ball is insufficient. In addition, a low trajectory of the ball may hinder increase of the carry.
According to the golf club head disclosed in JP-A-2002-119625, the crown portion is bent upward as soon as a ball is hit, so that the repulsion of the ball is enhanced. However, in the golf club head disclosed in the same publication, the rear portion of the golf club head is also thin so that the moment of inertia is relatively small.
In the golf club head disclosed in JP-A-Hei.7-155410, the specific gravity of the head rear portion is so heavy that the head is badly balanced in weight.
In the golf club head disclosed in JP-A-Hei.7-112041, the side portion is continuously integrated with the head rear portion and the head front portion including the face portion, so that the bending of the crown potion when a ball is hit is not always sufficient.